Instrument for manipulating components of joint prostheses

ABSTRACT

An instrument for manipulating, detachably holding and placing an insert portion of a joint socket prosthesis into an outer shell of a said prosthesis. The instrument includes a handle and a holding tool. The holding tool includes two or more grasping claws which extend radially from the longitudinal axis of the handle over the insert, and serve to engage the insert to the holding tool. The handle is elongated and slideably positioned within a longitudinal bore or hole in the holding tool and typically includes a plunger. The insert is released when an operator causes the handle to slide within the holding tool towards the insert with sufficient force to disengage the insert from the grasping claws.

The invention relates to an instrument for handling an insert shell andfor inserting it into an outer shell of a two-part joint socketprosthesis according to the preamble of the first claim.

Joint prostheses in which one joint partner is constructed as a socketand the other joint partner is constructed as a spherical head which isrotatably mounted in the socket are known in particular from shoulderand hip-joint prostheses. These prostheses are, as a rule, of modularconstruction. This means, for example, that the joint socket has twoparts and comprises an outer shell, which is inserted into the bone, andan insert shell, which is inserted into the outer shell and produces thejoint surface, the sliding surface for the other joint partner. Theinsertion of the sliding shell into the outer shell takes place, as arule, by means of press fit. For this purpose, it is necessary for theinsert shell to be aligned very precisely with respect to the outershell in order to avoid tilting during insertion. Apart from animprecise association of the joint surface with respect to the sphericalhead, damage to the insert shell can occur in the case of a tiltedinsertion. In particular, insert shells made of ceramic material canbreak or even shatter.

If the insert shells are inserted by the surgeon by hand, the handlingin the area around the operative wound is difficult because of thesurgeon's gloves being wet with body fluids and because of the lack of aclear view. For this reason, it is known to provide instruments whichimprove the handling of insert shells to be inserted. A handlinginstrument for joint components having joint surfaces is known fromGerman Utility Model DE 297 02 093 U1, which handling instrument has ahandle portion and a suction element arranged on the end thereof, whichsuction element comprises a sealing element contained therein which canbe placed in a sealing manner against the joint surface of the jointcomponent and, as a result of this, forms with this joint surface aclosed suction chamber, and also a device which lowers the pressure ofthe suction chamber. This handling instrument is placed with the sealingelement on the joint surface of the insert shell to be inserted, thepressure in the suction chamber is lowered and, as a result of this, theinsert shell is picked up by suction. After the insertion of the insertshell, the pressure is raised again and the handling instrument isautomatically detached from the inserted insert shell.

The known handling instrument, however, offers no certainty that theinsert shell can be put on to the outer shell with the required accuracyand that, as a result of this, tilting can be avoided. Apart from this,the known handling devices are long (up to 40 cm). They are thereforeunwieldy and are thus lacking in the required sensitivity during theinsertion process.

The underlying object of the present invention is to introduce aninstrument for handling an insert shell and for inserting it into anouter shell of a two-part joint socket prosthesis, with which instrumenta simple positioning and a tilt-free insertion are possible.

The object is achieved with the aid of the characterizing features ofthe first claim. Advantageous developments of the invention are claimedin the subclaims.

The instrument in accordance with the invention for handling an insertshell and for inserting it into an outer shell of a two-part jointsocket prosthesis comprises a handle with a holding tool connectedthereto. The holding tool for the insert shell can be handled easily bymeans of the handle. The holding tool has at least two gripping dogs.These extend substantially radially with respect to the longitudinalaxis of the handle. The claws of the gripping dogs rest on the end-facecircumferential surface of the insert shell to be inserted.

As a result of the arrangement of the gripping dogs and their claws, theinsert shell is held such that it is aligned precisely concentricallywith respect to the longitudinal axis of the handle and at right anglesto this axis. As a result of this, a precise alignment of the insertshell during insertion is possible for the surgeon. Apart from this, theshort structure of the instrument gives the surgeon the requiredsensitivity during the insertion process.

The claws of the gripping dogs grip around the tapering outer surface ofthe insert shell by the same length in each case, and to the extentthat, on the one hand, reliable holding but also, on the other hand,easy ejection from the claws are possible. The ejection of the insertshell from the gripping dogs of the holding tool takes place by means ofa plunger, which is mounted in a sliding manner in a bore which extendsconcentrically with respect to the longitudinal axis of the handle. Whenthe plunger is slid in the direction of the insert shell, the latter ispushed out of the claws of the gripping dogs and can be pressed into theouter shell of the joint socket prosthesis.

In a development of the invention, the claws of the gripping dogs haveend faces which extend at right angles to the longitudinal axis. Theseend faces are used for placing on the end face of the outer shell.Because the claws on the gripping dogs are all the same length, when allof the dogs are placed on to the end face of the outer shell, the insertshell is positioned precisely for its insertion. This development of thegripping dogs with which, in the difficult surroundings of the operativewound, the surgeon can position the insert shell reliably and preciselyfor the insertion, is an advantageous aid for the surgeon.

In order that no impairment of the position of the insert shell takesplace during the positioning of the instrument with the insert shell onthe outer shell, the length of the claws is at least dimensioned in sucha way that when they are placed on to the end face of the outer shell,the insert shell held by them still has no clamping contact with theouter shell. In this way, a correction of the positioning is possible atany time. This is ended when all of the dogs rest with their end faceson the end face of the outer shell.

In a further development of the invention, the dogs are made of anelastic material in order that the insert shell which is held can easilybe pushed out of the holding tool. A further advantage consists in thatinsert shells which differ from each other only slightly in terms oftheir diameters can be held by one and the same holding tool.

In another development of the invention, the claws of the gripping dogsare produced from an elastic material. Particularly in the case ofinstruments which are used only once, the claws can be constructed insuch a way that they even deform permanently when the insert shell ispushed out of the gripping dogs.

In a further advantageous development of the invention, the handle has arecessed grip. This recessed grip renders possible, for example, theclamping of the handle between two parallel fingers, for example themiddle finger and the ring finger or the index finger and the middlefinger. The recessed grip can be U-shaped, for example, and extendaround the entire handle, so that optimal holding of the instrument inthe hand of the surgeon is possible in any possible alignment. Thepushing-out of the insert shell can then, for example, take place bymeans of the thumb or the upper hand.

In order that the plunger does not exert a point-focussed load on theinsert shell during the ejection of the insert shell from the grippingdogs, it is advantageous if the end thereof has at least one plate withwhich it is supported in a ring-shaped manner on the insert shell. Sucha plate has the advantage that the plunger can be used for insert shellswith different joint-surface diameters.

In another development of the invention, the plunger has, on its end, astamping head which is matched to the joint surface of the insert shell.The stamping head then has the shape of a spherical segment, the radiusof which corresponds to the radius of the joint surface. Such a plungercan admittedly be used only for one diameter of an insert shell, but hasthe advantage that it distributes the force to be applied duringinsertion over a large surface and evenly on to the insert shell.

As a rule, the pressing of the insert shell into the outer shell iscarried out manually by the surgeon. However, for the final fixing, asubsequent blow with a striking tool may be required. In such a case,the instrument in accordance with the invention also offers apossibility of applying such a fixing blow in a targeted manner on tothe insert shell. As a result of the precise alignment of the instrumentwith respect to the outer shell and thus of the insert shell withrespect to the outer shell, the forces applied by the blow areintroduced into the insert shell evenly and precisely in accordance withtheir purpose.

The invention is explained in greater detail with the aid of anexemplifying embodiment.

FIG. 1 shows the instrument in accordance with the invention with aninsert shell to be inserted in the holding tool;

FIG. 2 shows a section along the axis through the handle of theinstrument, as drawn in in the Figure; and

FIG. 3 shows a sectional drawing corresponding to FIG. 2 with a furtherdevelopment of the plunger.

The representation in the figures is on an enlarged scale. In FIG. 1, 1denotes the instrument in accordance with the invention for handling andfor inserting the insert shell 2 held by it. The instrument 1 comprisesa handle 3 and a holding tool 4. In the present exemplifying embodiment,the holding tool 4 has three gripping dogs 5 which extend substantiallyradially from the longitudinal axis 6 of the handle 3. In the sectionaldrawing of FIG. 2, this can be seen with the aid of the right angle 7.In the present exemplifying embodiment, the gripping dogs are arrangedat equal angular distances →, but this is not absolutely necessary.

The gripping dogs 5 have claws 8 which grip over the tapering outersurface 9 of the insert shell 2. In order to take into account theconical shape of the outer surface 9 of the insert shell 2, the claws 8each have an undercut 13. The claws 8 are all of the same length 10. Inorder that precise positioning and alignment of the insert shell 2 withrespect to the outer shell is possible, the bearing surfaces 14 of thegripping dogs 5, which bearing surfaces rest on the end face 15 of theinsert shell 2, are at right angles to the longitudinal axis 6 of thehandle 3. Their extension intersects the axis 6 at a right angle 7, asshown in FIG. 2. This renders possible a precise placing of theinstrument on to the end face of the outer shell, as is evident fromFIG. 2.

In the present exemplifying embodiment, the gripping dogs 5 are elastic,so that when there is a pressure on the insert shell 2 in a directionout of the instrument 1, the claws 8 are bent outwards and release theinsert shell 2.

The pushing of the insert shell 2 out of the holding tool 4 takes placeby means of a plunger 16. The plunger 16 is mounted in a bore 17 whichextends concentrically with respect to the longitudinal axis 6 in thehandle 3. In the present exemplifying embodiment, the plunger 16 has aplate 18 at the end which faces the insert shell 2. The outercircumference 27 of this plate rests in a ring-shaped manner on thejoint surface 19 of the insert shell 2. The bearing surface liesconcentrically with respect to the longitudinal axis 6 of the handle 3,as is evident from FIG. 2. As a result of this, an even introduction ofpressing force into the insert shell 2 is ensured. If force is exertedon to the plunger 16 in the direction of the arrow 20, the gripping dogs5 release the insert shell 2 because of their elasticity.

The handle 3 has a U-shaped recessed grip 21, which extendsconcentrically around the handle. It is shaped such that the handle canbe held, in particular, between two parallel fingers. It is thenpossible to press on the end face 22 of the plunger 16 with the upperhand or with the thumb, and to push the insert shell 2 out of theholding tool 4. A cap 23 on the end face 22 of the plunger 16 has adiameter which is such that the plunger cannot slide through the bore 17when the insert shell 2 is pressed into the outer shell. Apart fromthis, this cap 23 protects the shank 22 in the case of possible blowswith a striking tool, and thus prevents chipping or splintering of theforward side edges of the plunger 16.

FIG. 2 shows a longitudinal section through the instrument 1, and theinsert shell 2 held by it, in the positioning position on an outer shell24. The course of the section is indicated by II—II in FIG. 1. Itextends through two adjacent gripping dogs 5.

In FIG. 2, the instrument 1, with the insert shell 2 held by it, isplaced with the end faces 11 of the claws 8 on the end face 25 of theouter shell 24. The insert shell 2 is positioned in the outer shell 24.Once all of the end faces 11 of the claws 8 have been placed on to theend face 25 of the outer shell 24, precise centring and positioning ofthe insert shell 2 is ensured.

As is evident from the sectional drawing, the claws 8 grip over theouter surface 9 of the insert shell 2, in the edge region thereof, bythe same length 10. This length coincides with the length of the claws8. The length 10 of the claws 8 is chosen such that when their end faces11 rest fully on the end face 25 of the outer shell 24, there is stillno clamping contact between the outer surface 9 of the insert shell 2and the inner surface 26 of the outer shell 24.

Not until the plunger 16 is activated by an application of force in thedirection of the arrow 20 will the gripping dogs 5 release the insertshell 2 because of their elasticity. In the present exemplifyingembodiment, the plunger 16 has, on the end which faces the insert shell2, a plate 18, the outer circumference 27 of which rests in aring-shaped manner on the joint surface 19 of the insert shell 2. As aresult of an application of force on to the plunger 16 in the directionof the arrow 20, the insert shell 2 is, after release, pressed by theholding tool 4 into the outer shell 24. A press fit takes place becauseof the conical shapes of the outer surface 9 of the insert shell 2 andof the inner surface 26 of the outer shell 24.

In FIG. 3, which reproduces a sectional drawing corresponding to FIG. 2,the plunger 16 has, on the end which faces the insert shell 2, astamping head 28 which is matched to the joint surface 19. Featureswhich are the same are provided with the same reference numerals in thisexemplifying embodiment. The stamping head 28 has the shape of aspherical segment, and its surface 29 corresponds precisely to that ofthe joint surface 19 of the insert shell 2. In this embodiment, alarge-surface and an even introduction of force onto the insert shell 2is possible.

The instrument 1 for handling an insert shell 2 can be produced from asterilisable material, for example from heat-resistant andchemical-resistant plastics, or from a metal having the same properties,so that reuse is possible. The instrument can, however, also be seen asa single-use tool, which is disposed of after use. In this case, it ispossible for an insert shell together with an instrument already holdingthe insert shell with its holding tool, to be made available to thesurgeon in sterile packaging. In this way, the manual insertion of theinsert shell into the holding tool of the instrument during theoperation is dispensed with, which makes the surgeon's operatingconditions easier and rules out damage to the sensitive joint surface ofthe insert shell.

What is claimed is:
 1. An instrument for manipulating, detachablyholding and placing an insert portion of a joint socket prosthesis intoan outer shell of a said prosthesis, said instrument comprising a handleand a holding tool, said holding tool further comprising at least twograsping claws extending substantially radially from the longitudinalaxis of said handle, said grasping claws extending over and engagingsaid insert with said holding tool, and said handle, being elongated andslideably positioned partially within a longitudinal bore in saidholding tool, further comprising a plunger distal to said insert,whereby said insert is released when an operator causes said handle toslide within said holding tool towards said insert with sufficient forceto disengage said insert from said grasping claws.
 2. The instrument ofclaim 1, wherein said grasping claws further comprise hooks, said hookshaving end faces which extend at right angles to the longitudinal axisof said handle, said end faces being capable of radially aligning withand contacting a corresponding face on a circumferential surface of saidinsert.
 3. The instrument of claim 1, wherein said hooks are dimensionedsuch that when said instrument contacts said corresponding face, aconical outer surface of said insert has no clamping contact with aninner surface of said outer shell.
 4. The instrument of claim 1, whereinsaid grasping claws comprise an elastic material.
 5. The instrument ofclaim 1, wherein said hooks comprise an elastic material.
 6. Theinstrument of claim 1, wherein said handle has a recessed grip.
 7. Theinstrument of claim 6, wherein said recessed grip is U-shaped andcircumferential.
 8. The instrument of claim 1, wherein the portion ofsaid plunger proximal to said insert further comprises a plate, theouter circumference of said plate capable of being placed on an insidesurface of said insert.
 9. The instrument of claim 1, wherein theportion of said plunger proximal to said insert further comprises astamping head having a shape complementary to an inside surface of saidinsert.